Hello all. I have a 102" ss whip attached to my deck rooftop (metal). I used a bumper mount to attach it to the metal roof. My dilema is that it gets out around 10 miles (farthest as of now) to the north, west, and east well. The peak of my roof seems to block it from getting out to the south more than about 2.5 miles. My swr is 1.1 on ch1 and 1.3 on ch40. The metal roof is acting as a ground plane. My question is can I attach a 10' chain link fence post to the side of my metal roof (where my mount is currently attached) so I can get up around 18' without loosing my ground plane? If I used metal fence post and metal u-bolts I could keep everything grounded to deck (which is grounded to a 8' copper ground rod I installed in the ground? I am aware that there are probably better antennas than what I have, but my A99 stuck out like a sore thumb. I don't want to draw too much attention from neighborhood association. The 102" ss whip the way it sits blends in pretty well. I just am loosing my southside reception with the blockage of my roof peak. I just want a bit better reception to the south where I do most of my travels. My 6 year old son and I have fun talking to each other with this setup. Thanks for any tips, or advice.
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102" base cb antenna needs advice
- Thread starter griggsb
- Start date
You need a number of 1/4 wave radials. Don't count on a metallic roof to do what the radials will do. AND you might need to raise the antenna up a bit so that the radials aren't tilted up. What are the dimensions of this metal roof? Is it all one piece of metal, or is it several separate pieces (that will all have to be bonded together)?
Doesn't matter what your SWR is. A dummy load has low SWR.
Space the radials equally around a circle. More is better, but never less than four.
Doesn't matter what your SWR is. A dummy load has low SWR.
Space the radials equally around a circle. More is better, but never less than four.
Raising the antenna up on a metal mast the antenna will attempt to use the mast as a ground plane. The metal roof will also be used, however, being many feet below the antenna it will not work well if it has much of an effect at all.
I would run three or four radials from the elevated position and angle them downwards off of the mast at the base of the antenna. These radials can be more 102" whips or can be wires attached to the base of the antenna and 9' long held with non conducting rope of some sort or at the very least something that is not connected electrically to them. The second method can double as a guy wire system if needed or you want extra support.
The DB
I would run three or four radials from the elevated position and angle them downwards off of the mast at the base of the antenna. These radials can be more 102" whips or can be wires attached to the base of the antenna and 9' long held with non conducting rope of some sort or at the very least something that is not connected electrically to them. The second method can double as a guy wire system if needed or you want extra support.
The DB
I think the biggest 'hang-up' would be keeping your antenna 'stealthy', not very noticeable. No coverage to the South? Move it to where it can 'see' to the South. But then, given your limitations, it probably won't 'see' some other direction. Raising it higher is one way of doing it.
That 102" whip is only half of the antenna, the 'groundplane', counterpoises, radials, or car body is the other half, and you aren't providing it. As already mentioned, there are a number of ways to do that providing of the 'other half'. One way of disguising an antenna is to put a bird house on top of it. Not too practical/possible with a 102" whip though.
Good luck.
- 'Doc
That 102" whip is only half of the antenna, the 'groundplane', counterpoises, radials, or car body is the other half, and you aren't providing it. As already mentioned, there are a number of ways to do that providing of the 'other half'. One way of disguising an antenna is to put a bird house on top of it. Not too practical/possible with a 102" whip though.
Good luck.
- 'Doc
I acid dipped my SS whip with PCB Etchant and it no longer is shiny. Now it has a dull gray finish that blends better than the original finish.
Have you thought about a simple dipole laying along your roofline?
Have you thought about a simple dipole laying along your roofline?
Thanks for the replies guys. My metal roof is 20' x 15'. I may try to mount it on a metal fence post (attached to metal roof) with the radials. What gauge copper do I need for the radials? Will the radials (on north side of my house) be blocked in the same way by the peak of my roof (for the south communications)? Maybe the dipole would be worth trying. Anybody have a diagram, and a list of what I might need to build one? I'm not at all familiar with the dipole design. Aproximatly how far might I talk out with the dipole barefoot? Thanks again to all.
With the obstacle you pretty much have two choices, you can raise the antenna above it or move the antenna to the other side of it. Moving the antenna will simply change the direction of the blocked signal.
When it comes to local omnidirectional range again there are two things you can do. First and the more effective would be to raise the antenna up to a higher location. The other is to get a longer antenna.
A dipole is a simple antenna to build, at least if you mount it horizontally. At CB frequencies it is two wires that are about 9' long, one is connected to the center conductor of a coax, and the other is connected to the shielding of the coax. The problem is if you mount one of these horizontally (as is typical) it does not act like an omnidirectional antenna and being a different polarization (big word I know, just means how the antenna is oriented) the signals going from this type of antenna to a vertical antenna will be attenuated greatly (will appear to be weaker). You could solve this problem by hanging it vertically, for instance in a tree. What kind of range this type of antenna will get you depends on several factors, from what kind of soil is in the area, what is blocking the signal, if your at the top or bottom of a hill, local RF conditions you have no control over, ect. That being said, those same factors will affect pretty much any antenna you put up.
The DB
When it comes to local omnidirectional range again there are two things you can do. First and the more effective would be to raise the antenna up to a higher location. The other is to get a longer antenna.
A dipole is a simple antenna to build, at least if you mount it horizontally. At CB frequencies it is two wires that are about 9' long, one is connected to the center conductor of a coax, and the other is connected to the shielding of the coax. The problem is if you mount one of these horizontally (as is typical) it does not act like an omnidirectional antenna and being a different polarization (big word I know, just means how the antenna is oriented) the signals going from this type of antenna to a vertical antenna will be attenuated greatly (will appear to be weaker). You could solve this problem by hanging it vertically, for instance in a tree. What kind of range this type of antenna will get you depends on several factors, from what kind of soil is in the area, what is blocking the signal, if your at the top or bottom of a hill, local RF conditions you have no control over, ect. That being said, those same factors will affect pretty much any antenna you put up.
The DB
Not in any kind of order...
That metal rood sounds like it could be used as the other half of your 102" whip, it's big enough. If the rest of the roof it's next to isn't metal it would be like any other groundplane type antenna mounted in the same place, almost. Since it's below the rest of the roof, the roof will probably 'block' a little signal to/from that direction, maybe. It'd be about like it is now, as a guess.
A dipole antenna (1/2 wave, twice as 'long' as that 102" whip) isn't a complicated antenna at all. It would have to be tuned (adjust the length) just like any other antenna. The biggest thing with dipoles is that they can be polarized, either horizontally or vertically, depending on how they are 'strung up'. That polarization can mean a big difference in what can be heard. Two antennas not of the same polarization won't 'hear' each other very well. If it's put up horizontally then it's horizontally polarized. If you just hang it from one end, it'll be vertically polarized. Almost all mobile antennas are vertically polarized so they wouldn't work together too well. That certainly does not mean that dipoles aren't any good, they certainly are. But polarization does affect how 'good' they are.
Groundplanes, of whatever kind, work best if they are at, or very close to the feed point of the vertical part of the antenna. The further the feed point is from that 'other half' of the antenna the less 'good' it becomes. Just something to consider when doing the mounting etc.
If there's something 'blocking' you in one direction and you move to the other side of that 'something', you'll probably be 'blocked' in the other direction, maybe. I wouldn't bet a lot on it, but it's something I think I'd bet on, you know? That's a fairly common occurrence. The 'best' way of getting around that is by getting on top of whatever that 'something' is. That's also probably not the most practical thing to do for whatever reason.
Hope this helps a little, it certainly doesn't cover all the possibilities though.
- 'Doc
That metal rood sounds like it could be used as the other half of your 102" whip, it's big enough. If the rest of the roof it's next to isn't metal it would be like any other groundplane type antenna mounted in the same place, almost. Since it's below the rest of the roof, the roof will probably 'block' a little signal to/from that direction, maybe. It'd be about like it is now, as a guess.
A dipole antenna (1/2 wave, twice as 'long' as that 102" whip) isn't a complicated antenna at all. It would have to be tuned (adjust the length) just like any other antenna. The biggest thing with dipoles is that they can be polarized, either horizontally or vertically, depending on how they are 'strung up'. That polarization can mean a big difference in what can be heard. Two antennas not of the same polarization won't 'hear' each other very well. If it's put up horizontally then it's horizontally polarized. If you just hang it from one end, it'll be vertically polarized. Almost all mobile antennas are vertically polarized so they wouldn't work together too well. That certainly does not mean that dipoles aren't any good, they certainly are. But polarization does affect how 'good' they are.
Groundplanes, of whatever kind, work best if they are at, or very close to the feed point of the vertical part of the antenna. The further the feed point is from that 'other half' of the antenna the less 'good' it becomes. Just something to consider when doing the mounting etc.
If there's something 'blocking' you in one direction and you move to the other side of that 'something', you'll probably be 'blocked' in the other direction, maybe. I wouldn't bet a lot on it, but it's something I think I'd bet on, you know? That's a fairly common occurrence. The 'best' way of getting around that is by getting on top of whatever that 'something' is. That's also probably not the most practical thing to do for whatever reason.
Hope this helps a little, it certainly doesn't cover all the possibilities though.
- 'Doc
Ok. With around a 10' vertical mounted chain link top rail I can get 102" whip around 6' above peak of roof (an approximate guess). The mast will attach from metal roof with a ubolt and be braced on the bottom to the deck. Should hold up to the wind that way. As far as radials go could I "Y" 2 or 3 radials from my mast? Will it affect reception if my copper radials are touching my metal roof? I would be running them from center of mast and sloping downhill. With my antenna being located on the side of my roof I wouldn't be able to run radials all the way around my mast. Even if I relocated mast/antenna to peak of roof at chimney it would be the same problem. I still could only "Y" off radials to one side. Bad idea? All this trouble just so I can talk to my boy LOL. Thanks so much guys.
The propagation pattern of your proposed antenna would be effected, it would be a carotid pattern ( heart shaped) with the "null" in the direction lacking the ground radial. If this null was toward the roof and your roof was metal, then you could run a braided ground strap from the missing ground radial to the roof, this will not elimate the null but it would reduse it. Think of your propagation pattern like a doughnut, your antenna is in the middle of the doughnut, however, your doughnut looks more like a heart than a round doughnut. A verticle 1/4 antenna has a radiation pattern angle of about 50 degrees starting at the ground plane. This is known as the ground wave, it a good idea to keep this in mind when setting up an antenna. Your propagation pattern is the entire signal 360 degrees around your antenna, this is effected by ground radials, trees, buildings or anything else that can obstruct a signal.
Another thing you could do to increase the ground capability around your mast. This is done by burying ground radials at about every 10 degrees around the base of the mast and having these radials attached to the mast. This is done in area that have poor ground conductivity. This type of ground radials should be a minimum of 1/2 wavelength, longer is better.
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The radials not being symmetrical will affect the over all radiation pattern, true. But, it'll be a far cry from being cardioid, or pear shaped. Sort of an off centered wide-oval shape, but not directional to any significant degree. In most cases you'll never know things aren't as they should be. In cases where there's a significant, or recognizable, or hear able difference in the radiation pattern there will definitely be something besides the radials making it so.
- 'Doc
- 'Doc
dipole
a dipole works but on your roof it will be horizinal talking.why not just put the gray 102 at the center of the peak of the house?and if stealth was the main idea.then 18' in air kills that too.also as stated above make groundplan elements and at 18' it will dif talk 360 then
a dipole works but on your roof it will be horizinal talking.why not just put the gray 102 at the center of the peak of the house?and if stealth was the main idea.then 18' in air kills that too.also as stated above make groundplan elements and at 18' it will dif talk 360 then
Does the SWR tune on 10m - or the CB band?
If you are using it for the CB band; then you might need to make it a smidgle taller. More like 108".
The 3 - or 4 - 104" radials will tune best at a 45 degree down angle. Keep them separated away from your metal roof. If you need sturdier ground planes, then you might consider using 1/2" EMT conduit. The sell for about $2 apiece for each 10ft length. Just cut them down to size and mount them at the 45 degree angle. Might put the antenna a bit higher to clear the roof - too . . .